Bud outgrowth is controlled by environmental and endogenous factors. Through the use of the photosynthesis inhibitor norflurazon and of masking experiments, evidence is given here that light acts mainly as a morphogenic signal in the triggering of bud outgrowth and that initial steps in the light signaling pathway involve cytokinins (CKs). Indeed, in rose (Rosa hybrida), inhibition of bud outgrowth by darkness is suppressed solely by the application of CKs. In contrast, application of sugars has a limited effect. Exposure of plants to white light (WL) induces a rapid (after 3-6 h of WL exposure) up-regulation of CK synthesis (RhIPT3 and RhIPT5), of CK activation (RhLOG8), and of CK putative transporter RhPUP5 genes and to the repression of the CK degradation RhCKX1 gene in the node. This leads to the accumulation of CKs in the node within 6 h and in the bud at 24 h and to the triggering of bud outgrowth. Molecular analysis of genes involved in major mechanisms of bud outgrowth (strigolactone signaling [RwMAX2], metabolism and transport of auxin [RhPIN1, RhYUC1, and RhTAR1], regulation of sugar sink strength [RhVI, RhSUSY, RhSUC2, and RhSWEET10], and cell division and expansion [RhEXP and RhPCNA]) reveal that, when supplied in darkness, CKs up-regulate their expression as rapidly and as intensely as WL Additionally, up-regulation of CKs by WL promotes xylem flux toward the bud, as evidenced by Methylene Blue accumulation in the bud after CK treatment in the dark. Altogether, these results suggest that CKs are initial components of the light signaling pathway that controls the initiation of bud outgrowth.

• MeSH
• Models, Biological MeSH
• Time Factors MeSH
• Cytokinins metabolism   pharmacology   MeSH
• Meristem genetics   growth & development   metabolism   MeSH
• Reverse Transcriptase Polymerase Chain Reaction MeSH
• Gene Expression Regulation, Plant drug effects   radiation effects   MeSH
• Plant Growth Regulators metabolism   pharmacology   MeSH
• Rosa genetics   growth & development   metabolism   MeSH
• Plant Proteins genetics   metabolism   MeSH
• Signal Transduction drug effects   genetics   radiation effects   MeSH
• Light * MeSH
• Darkness MeSH
• Plant Shoots genetics   growth & development   metabolism   MeSH
• Gene Expression Regulation, Developmental drug effects   radiation effects   MeSH
• Xylem genetics   growth & development   metabolism   MeSH
• Publication type
• Journal Article MeSH